1. Field of the Invention
The present invention generally relates to an automatic transmission. More specifically, the present invention relates to a stepped automatic transmission that can be used as a transmission in a vehicle.
2. Background Information
In the past, automatic transmissions have been proposed in which three groups of planetary gears are used to establish seven forward speeds. For example, automatic transmissions of this type are disclosed in Japanese Laid-Open Patent Publication No. 2004-176765 and U.S. Pat. No. 6,648,791. In particular, Japanese Laid-Open Patent Publication No. 2004-176765 discloses a progressive seven-speed automotive transmission that has an advantage in transmission efficiency and reduced gear noise by uses three groups of durable, single-pinion planetary gears and six friction elements without the pinion gear being reduced in diameter. Similarly, U.S. Pat. No. 6,648,791 discloses an automotive transmission in which three groups of single-pinion planetary gears and five friction elements are used to establish six to eight forward speeds
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved automatic transmission. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.